Questioner
One question I've been thinking about a lot, and that is the black bladed sword. Is there just one sword, or is there one for each world, that [works with?] different...like Shard powers, or is it just one sword that can work with all?
Brandon Sanderson
[Nightblood] is something special. A long time ago, some people from the Warbreaker world came to Roshar, saw Shardblades, thought, "We can do this," went home and tried to make one. And that is Nightblood. And it went horribly horribly wrong. And so they didn't make any more, except now, Azure's sword is somewhat related. But that is the origin of Nightblood. Trying to make a Shardblade out of a different magic system.
Idaho Falls signing (July 21, 2018)
Questioner
Does the sword with *inaudible* Azure...
Brandon Sanderson
Mmhmm?
Questioner
Is it a lot like Nightblood, maybe?
Brandon Sanderson
It shares some features, but is different.
Orem signing (Dec. 21, 2017)